As shown in FIG. 13, an electric field type fingerprint identification apparatus according to the conventional technology includes at least one fingerprint identification basic unit. The fingerprint identification basic unit includes an electrode plate 71, a first transistor 72 serving as a controlled switching device, a second transistor 73 serving as another controlled switching device and an electric charge amplifier 74. During fingerprint identification, the first transistor 72 is firstly switched on to charge the electrode plate 71 and reset the electric charge amplifier 74. Then, the first transistor 72 is switched off and the second transistor 73 is switched on to transfer an electric charge on the electrode plate 71 to an output end of the electric charge amplifier 74. In this way, a feature image of a fingerprint is determined based on different change quantities of the electric charge. The electric field type fingerprint identification apparatus according to the conventional technology has the following defects and disadvantages.
1. Two transistors serving as the controlled switching devices are adopted to achieve a basic fingerprint identification function, hence a structure of the fingerprint identification basic unit is complicated and a device cost is high.
2. Diverse design solutions can not be obtained based on an application requirement, due to a single form of the circuit.
3. Mutual interference exist between electric fields of fingerprint identification basic units. Parasitic capacitors exist between the fingerprint identification basic units. During charging and discharging the electrode plate, the quantity of the electric charge may be changed by the parasitic capacitors. And since the change quantity of the electric charge caused by the parasitic capacitors is unmeasurable, the mutual interference exist between the electric fields of the respective fingerprint identification basic units, thereby affecting accurate measurement of the change quantity of the electric charge and thus affecting a result and accuracy of the fingerprint identification.
4. A fingerprint of a prosthesis finger can not be determined and distinguished by the fingerprint identification apparatus according to the conventional technology.